What people can buy in the Augur crowdsale is Reputation (REP). REP tokens can be used to report on events.

From what I understand, this is roughly how it works:1. someone adds a prediction market with a statement, like: "The Bitcoin price will be at $1000 before the end of the year."2. gamblers bet on this market (yes or no) - they pay a small fee3. after the event occurred, REP holders will report on the event: it happened or it didn't happen4. the wagered money will be divided over the winning gamblers, the fees will be divided over the majority of the REP holders

REP holders that chose the wrong answer or that didn't report, will lose REP.